New generation of four-cylinder diesel engines from
Mercedes-Benz leads the way

Stuttgart Germany April 10, 2008; What better way to mark the 150th anniversary of Rudolf Diesel's
birth than a brand new generation of four-cylinder diesel engines from
Mercedes-Benz which outstrip all previous benchmarks for performance,
torque, emission properties and, most notably, fuel economy in their
segment? In its most powerful variant, the new four-cylinder unit musters
up 150 kW/204 hp from its 2143 cubic centimetres, meaning that it delivers
around 20 per cent more power than the engine it replaces. At the same
time, peak torque has risen from 400 Nm to 500 Nm, equating to an increase
of 25 per cent. Despite the 25 kW increase in output, the new four-cylinder
diesel burns substantially less fuel than its predecessor, which was itself
highly economical. As a consequence, CO2 emissions are reduced by as much
as 13 per cent and the new four-cylinder diesel unit already complies with
the future EU5 emissions standard.

The new four-cylinder diesel generation from
Mercedes-Benz can be briefly summed up as follows: greater power, greater
economy, greater cleanliness. The new power unit from the Untertürkheim
plant needs to be explained at greater length to be fully appreciated,
however. It really does charter territory from which diesel engines - and
four-cylinder units particularly so - have previously been excluded. It
redefines standards for power output and torque on the one hand and for
fuel consumption and exhaust emissions on the other, setting benchmark
figures which no other comparable series-production engine is able to match
at the current time.

The technical advance which the design engineers at
Mercedes-Benz have achieved with this new four-cylinder diesel is not only
evident on paper, its effects can also be experienced to an intense degree
behind the wheel. As far as the figures are concerned, the most powerful
variant of the new diesel engine extracts 150 kW/204 hp from its
displacement of 2143 cubic centimetres. This represents an increase of some
20 per cent compared to its predecessor, despite the displacement being
almost identical. Meanwhile, the engine's peak torque has been upped by 25
per cent from 400 Nm to 500 Nm. The power-to-displacement and
torque-to-displacement ratios of the new engine from Untertürkheim make
just as impressive reading, with figures of 70 kW/95.2 hp and 233.3 Nm per
litre respectively (the figures for its predecessor by comparison: 58.2
kW/79.2 hp and 186.2 Nm per litre of displacement).

Lower fuel consumption despite substantial
gain in output

The engineers also took care to ensure the new
diesel engine is a paragon of fuel efficiency. In spite of the
substantial power boost of 25 kW, the engine makes even more frugal use of
diesel than its predecessor, which was itself a most modest consumer of
fuel. This is immediately apparent from the fuel consumption figures for
the C-Class, in which the powerpack will be making its debut in the autumn.
When fitted in the C-Class, the new 150-kW unit burns just 5.4 litres of
diesel per 100 kilometres (NEDC), 0.5 litres less than previously. And when
powered by the 125-kW/170-hp variant that is also newly available, the
C‑Class returns even lower fuel figures of 5.1 litres for every 100
kilometres (a drop of 0.8 litres). As a consequence, CO2 emissions are
reduced by 8 and 13 per cent respectively to 143 and 136 g/km. The
Mercedes-Benz engineers have also succeeded in further reducing the amount
of untreated engine emissions. Even without an active denoxification
process, the new four-cylinder diesel already meets the future EU5
emissions standard.

"This takes our new four-cylinder unit into a realm
which has so far been the preserve of three-litre six-cylinder diesel or
large V8 petrol engines - all combined with exemplary fuel economy,"
commented Dr. Thomas Weber, who is responsible for Group Research and
Development at Mercedes-Benz Cars on the Daimler AG Board of
Management.

Tangible progress and intense motoring
pleasure

Drivers are able to savour the advances that have
been made with all of their senses. The new drive unit has a powerful feel
to it, its response is agile, it delights with its tremendous pulling power
and impresses with admirable levels of smoothness for a four-cylinder
engine. It enables sports-car-like performance, propelling the C-Class
Saloon from standstill to the 100-km/h mark in a mere 7.7 seconds. The
engine's supreme flexibility permits quick turns of speed for rapid
overtaking on country roads, taking just 9.4 seconds to pick up from 60 to
120 km/h. This all adds up to a high degree of fun at the wheel combined
with great economy.

Quite apart from its outstanding power output data,
the new drive unit also boasts markedly superior torque build-up from low
revs compared to the engine it replaces, along with a class-beating torque
characteristic curve. This means that the engine can be run extremely
economically at low rev speeds in routine driving situations.

The new diesel engine is set to supersede four
different powerplants in all, and will be fitted in a number of variants
across a wide range of model series, even including the Mercedes-Benz
Sprinter. Thanks its high power potential it has been possible to apply the
downsizing principle, where smaller engines with fewer cylinders are used
in order to lower fuel consumption very effectively. Thanks to the agility,
pulling power and optimum running characteristics of the new diesel drive
unit, the vehicles it is fitted in will continue to be able to live up to
the high standards of comfort and motoring pleasure expected of models from
Mercedes-Benz. Three different variants are initially planned for use in
passenger cars.

The key data

250 CDI

220 CDI

200 CDI

Number of cylinders

4

4

4

Valves per cylinder

4

4

4

Displacement, cc

2143

2143

2143

Bore/stroke, mm

83.0/99.0

83.0/99.0

83.0/99.0

Compression ratio

16.2:1

16.2:1

16.2:1

Output, kW/hp

150/204 at 4200 rpm

125/170 at 3200 -4800 rpm

100/136 at 3000 -4600 rpm

Torque, Nm

500 at 1600 - 1800 rpm

400 at 1400 - 2800 rpm

330 at 1600 - 2800 rpm
*)

*) with automatic transmission

The next chapter in the Mercedes-Benz diesel
success story

This new diesel powerplant is Mercedes-Benz's
resounding answer to questions over the future of motoring, and marks yet
another milestone in the evolution of diesel technology. At the same time,
the Stuttgart-based automotive manufacturer is perpetuating a long-standing
tradition. It was as long ago as 1936 that the diesel engine received its
world premiere in a passenger car from Mercedes-Benz - the now legendary
260 D. Ever since, Mercedes-Benz has been hard at work advancing and honing
the technology it pioneered. There have been many momentous occasions over
the years, including the first ever turbodiesel passenger car engine in the
Mercedes-Benz 300 SD (1977), the world premiere of four-valve technology
(1995), the first diesel-powered saloons with particulate filter system in
the US state of California (1985), common-rail direct injection technology
(1997), the maintenance-free diesel particulate filter (2003) which has in
the meantime become available for all Mercedes-Benz diesel models, as well
as the introduction of BlueTec technology (2006) for the cleanest-running
diesel engines in the world.

100,000 hours on the test rig and ten
million test kilometres

Mercedes-Benz is now adding the latest chapter to
this long-running success story with the arrival of its all-new,
groundbreaking four-cylinder diesel engine. After a 48-month development
period, during which time the design engineers employed the very latest
computer technology, the first prototype of the new engine was put into
operation in August 2005. Some 100,000 hours on the test rig were required
to elicit optimum performance characteristics from the new engine under all
conditions and regardless of the intended purpose. The power units were
subject to tough endurance testing, including acutely demanding cycles on
the test rigs that were designed to truly put them through their paces.
Over a distance of ten million test kilometres in a variety of vehicles,
the engine had to prove its mettle in the baking heat of the desert and the
icy cold of the polar regions, withstanding dust, mud, water and the very
harshest treatment in the process.

The new engine celebrates its premiere in autumn
2008, when the first power rating variant will be launched in just the
C-Class initially. The power unit is due to be deployed in various model
series from Mercedes-Benz, returning outstanding fuel consumption figures
in all cases. It can be installed both lengthways and crossways and is
envisaged for all-wheel-drive vehicles too. Naturally, the new engine can
be supplemented by the cutting-edge BlueTec emissions control system
developed by Mercedes-Benz, and it is also earmarked for use as a
fuel-efficient internal combustion engine in hybrid vehicles.

Innovative technologies without
parallel

The exemplary figures achieved by the new engine for
output and torque characteristics, economy, exhaust emissions and
smoothness are the result of a whole raft of innovative technologies.
These include a number of new developments, the likes of which cannot
currently be found in any other standard-production passenger car diesel
engine. The principal features of the new Mercedes diesel engine:

Two-stage turbocharging ensures high power output
and optimum torque delivery.

Fourth-generation common-rail technology with a
rail pressure that has been increased by 400 bar to 2000 bar, plus a new
piezoelectric injector concept featuring direct injector needle control
creates the ideal basis for more flexible injection timing, leading to
smoother engine running, lower fuel consumption and reduced
emissions.

The maximum ignition pressure is 200 bar which also
contributes to the high output.

Both the oil-spray nozzles and the water pump are
activated in accordance with requirements to save energy.

The camshaft drive is positioned at the rear in
order to enhance running refinement and satisfy the exacting pedestrian
protection requirements.

The engine block is made from cast iron, the
cylinder head from aluminium.

Two water jackets guarantee maximum cooling even at
the points of greatest thermal radiation; it is this that enables a
ignition pressure of 200 bar and such a high power-to-displacement
ratio.

The aluminium pistons slide up and down in
cast-iron barrels for minimum frictional resistance.

The connecting rods are made from forged steel, and
their weight has been optimised by the Mercedes engineers.

In the interests of vibrational comfort, the forged
crankshaft with its eight counterweights turns supported by five bearings.
The radii of the crankpins are rolled for high strength.

To compensate for the free vibration moments which
are inherent to four-cylinder inline engines there are two Lanchester
balancer shafts at the bottom of the engine block running in low-friction
roller bearings rather than conventional plain bearings.

A two-mass flywheel, featuring a primary flywheel
mass fixed to the crankshaft that is connected to the secondary flywheel
mass on the transmission by means of springs (technical term: spring-mass
system), isolates the crankshaft's vibration stimuli from the drivetrain,
thereby contributing to the engine's excellent smoothness.

Injection with the fourth generation of the
common-rail principle

The new diesel unit from Mercedes-Benz ushers in the
fourth generation of the tried-and-tested common-rail direct injection
technology. The distinguishing characteristic of the latest generation is
the increase of 400 bar in the maximum rail pressure, which now equals 2000
bar. This rise in pressure potential was of crucial importance for boosting
the engine's output to 150 kW/204 hp and its torque to 500 Nm, whilst at
the same time bringing about a marked improvement in the engine's untreated
emissions.

Piezoelectric injectors which are a completely new
development form one of the key components in the fourth-generation CDI
technology. They harness the ability of piezoelectric ceramic to alter its
crystalline structure with microsecond speed when an electrical voltage is
applied. The actual spatial movements produced are tiny however, For this
reason, the new injectors are fitted with a piezo stack, which is basically
made up of piezoelectric elements connected in series. In contrast to the
customary systems used to date, the movement of these elements controls the
injector needle directly and enables even greater alterations in volume
that are accurate to within a few thousandths of a millimetre. The benefits
of this are in increase in the available injection volume as well as
particularly fine and fast metering of the injection quantities. This
enables the fuel injection process to be adapted to the momentary engine
load and rev speed with yet greater exactness - by means of high-precision
multiple injections of fuel for example - which has a positive impact on
emissions, consumption and combustion noise. Plus, the engine runs even
more quietly when idling than its predecessor.

As a result of the innovative actuation concept,
injector operation is completely leak free. This dispenses with the need
for a leak oil line to return the negligible quantities of fuel that used
to accumulate unavoidably in the system on account of the operating
principle. This improves the injection system’s thermal circuit to
such an extent that, even at a rail pressure of 2000 bar, fuel cooling is
super-fluous to requirements. Not only does this save energy, it reduces
the high-pressure pump’s operating energy input by around one
kilowatt at high engine loads.

In order to continue to deliver optimum injection
quantities over the engine’s entire service life, an adaptive
learning function is able to compensate for any tolerance deviations that
may occur as a result of minimal component wear.

200 bar ignition pressure and optimised
combustion chamber

The fuel is injected into a combustion chamber with
a meticulously devised geometrical form that includes the
precision-calculated recesses in the piston crowns. Compared to the engine
it replaces, the combustion chamber has been made flatter and the diameter
somewhat larger. The compression ratio was reduced from 17.5 :1 to 16. 2 :
1. This optimises the combustion process by achieving a lasting reduction
in untreated emissions - NOx levels in particular have been cut
drastically.

One of the determining factors for maximum power
output and for fuel consumption at full throttle, from an emissions point
of view, is the maximum ignition pressure. With a pressure of 200 bar, the
new four-cylinder diesel from Mercedes-Benz is one of the top-ranking
passenger car diesel engines in this regard. To guarantee spontaneous
starting, the engine is fitted with ceramic glow plugs which attain a
temperature approximately 200 degrees Celsius higher than metallic glow
plugs (1250°C as opposed to 1050°C) and are virtually wear-free.
Mercedes-Benz put these glow plugs into series production for the first
time in the predecessor diesel engine.

Two-stage turbocharging for high torque at
all engine speeds

The new diesel unit draws the air it needs to
breathe from not one but two turbochargers, marking the first ever instance
of two-stage turbocharging in a series-manufactured passenger car diesel
engine from Mercedes-Benz. The aim of this concept is to eliminate the
inherent drawbacks of a single-stage turbocharger. These include, for
instance, the moment of inertia of a large turbocharger, which drivers may
perceive as sluggish start-off characteristics (turbo lag). What’s
more, it is virtually impossible to reconcile good start-off abilities and
maximum power along with low fuel consumption even at full throttle when
deploying just a single-stage turbocharger.

The compact-sized module for the new two-stage
turbocharging concept consists of a small high-pressure (HP) plus a large
low-pressure (LP) turbocharger. Both comprise a turbine and a
turbine-driven compressor, and are connected with one another in
series:

The HP turbine has a diameter of 38.5 mm and is
positioned directly in the exhaust manifold. The flow of exhaust gases
flows through this turbine first, causing it to rotate at speeds of up to
248,000 revolutions per minute.

Integrated into the HP turbine housing is a bypass
duct, which can be opened or closed by means of a charge-pressure control
flap triggered by an actuator. If the duct is closed, the entire exhaust,
the whole exhaust stream flows through the HP turbine, meaning that all of
the energy contained in the exhaust gases can be directed towards
propelling the HP turbine only. In this way, the optimum charge pressure
can be built up at low rev speeds.

As the engine speed increases, the charge-pressure
control flap opens to prevent the HP charger from becoming overloaded. A
portion of the exhaust stream now flows through the bypass duct to relieve
the load on the high-pressure stage.

Downstream from the HP turbine, the two exhaust gas
streams join up again, and any remaining exhaust energy drives the
50-millimetre LP turbine at a maximal speed of 185,000 revolutions per
minute.

To protect it against overload, the LP turbine also
features a bypass duct, which is opened and closed by means of an
actuator-controlled flap known as the "wastegate".

Once the engine reaches medium rev speeds, the HP
turbine's charge-pressure control flap is opened so wide that the HP
turbine ceases to perform any appreciable work. This allows the full
exhaust energy to be directed with low losses into the LP turbine, which
then does all of the turbine work.

The two compressors are likewise connected in series
and are in addition connected to a bypass duct. The combustion air from the
air cleaner first flows through the LP compressor (diameter 56.1 mm) where
it is compressed as a function of the LP turbine's operating energy input.
This pre-compressed air now passes into the HP compressor (diameter 41 mm)
that is coupled to the HP turbine, where it undergoes further compression -
the result is a genuine two-stage turbocharging process.

Once the engine reaches a medium rev speed, the HP
compressor can no longer handle the flow of air, meaning that the
combustion air would heat up too much. To avoid this, the bypass duct opens
to carry the combustion air past the HP compressor and directly to the
intercooler for cooling. In this case, the charge-pressure control flap is
completely open too, meaning that the HP turbine is no longer performing
any work. This is the equivalent of single-stage turbocharging.

The benefits of this elaborate, needs-driven control
of the combustion air feed with the aid of two turbochargers are improved
cylinder charging (for high output), meaning abundant torque even from low
rev speeds. Besides this, fuel consumption is lowered too. The upshot of
this as far as the driver is concerned is harmonious driving
characteristics with zero turbo lag, good torque delivery over the entire
rev band, tangibly superior performance, plus better communication between
engine and accelerator.

Intercooler and exhaust gas recirculation
have been optimised

The new turbocharger system is perfectly
complemented by an intercooler that has been enlarged compared to the
previous series-production version and now lowers the temperature of the
air - that has been first compressed and therefore heated up - by around
140 degrees Celsius, allowing a greater volume of air to enter the
combustion chambers.

After the intercooler, an electrically controlled
flap ensures precise regulation of the fresh air and recirculated
exhaust gas. So as to optimise the quantity of exhaust gas recirculated and
thereby achieve high recirculation rates, the exhaust gases are cooled down
as required in a powerful heat exchanger with a large cross-sectional area.
This combines with the HFM (hot-film air-mass sensor) modules, which are
integrated into the fresh-air supply and provide the engine management unit
with exact information on the current fresh air mass, to bring about a
substantial reduction in nitrogen oxide emissions. The results are highly
impressive: efficient engine warming, reduced emissions when engine is
still cold due to warmer combustion temperatures, reduced emissions when
engine is warm thanks to good EGR compatibility and good EGR cooling, no
tendency for deposits to build up, as well as a long service life. The
engine can be started at temperatures as low as approximately zero degrees
Celsius with no preglow waiting period, while the effective turbocharging
technology ensures that the engine runs stably without misfiring even when
cold.

Intake port shut-off for optimum air
supply

The combustion air subsequently flows into the
charge-air distributor module, which supplies air to each cylinder in a
uniform manner. Built into the distributor module is an electrically
controlled intake port shut-off which allows the cross-sectional area of
each cylinder's intake port to be smoothly reduced in size. This alters the
swirl of the combustion air in such a way as to guarantee that the charge
movement in the cylinders is set for optimum combustion and exhaust
emissions over the full spectrum of engine loads and rev speeds.

Rear-mounted camshaft drive

The list of the new four-cylinder diesel engine's
principal innovations also includes the rear-mounted camshaft drive. This
allows statutory pedestrian protection requirements to be fulfilled when
the engine is installed lengthways with the bonnet rising towards the rear.
The vibration stimuli originating from the crankshaft are furthermore lower
on the rear face of the engine than at the front, which benefits the
engine's exceptionally smooth running.

The valve timing mechanism is another new
development and reduces friction at the 16 intake and exhaust valves, which
are controlled by one overhead intake shaft and one overhead exhaust shaft
acting via cam followers featuring hydraulic valve clearance compensation.
The camshaft, Lanchester balancer as well as the ancillary assemblies are
driven by a combination of gearwheels and just a very short chain drive. It
was possible to reduce the increased noise levels usually associated with a
gearwheel drive by carrying out painstakingly detailed refinement.

Controllable water and oil pumps save
fuel

The electrically controllable water and oil pump
which can be activated in accordance with requirements are also unique
features for a standard-production diesel engine. Piston cooling is taken
care of by an oil pump with a central valve for controlling all four
piston-cooling sprayer units with their large oil-spray nozzles. The result
is identical basic thermal conditions for all cylinders. The generously
sized nozzles promise optimum piston cooling, even when operating under
full load, guaranteeing a long service life in the process. The oil pump's
controllable design additionally reduces the oil flow rate - and therefore
fuel consumption.

The controllable water pump is yet another
innovative new feature. Just like the controllable oil sprayer units, the
water pump also helps to quickly warm up both the combustion chamber and
the friction partners, at the same time lowering fuel consumption and
untreated emissions.

Development potential has not yet been
exploited to the full

In spite of its unrivalled power output, model
running characteristics and outstanding fuel consumption figures, the new
four-cylinder diesel engine from Mercedes-Benz holds yet further, untapped
potential. Development work is continuing on the possibilities offered by
ultra-flexible injection timing with a view to exerting an even more
positive effect on engine emissions.

In addition to this, combing the new star of the
diesel sector with other consumption-optimisation technologies - such as
those found in hybrid vehicles - will achieve further significant
reductions in fuel consumption.